Acoustic plaster is plaster which contains fibres or aggregate so that it absorbs sound.
Such plaster is applied in thicknesses of up to 1.5 inches. As compared with other sound insulation, it is easy to apply and is fireproof but it can be more fragile, being affected by physical stress and humidity. Acoustic plaster is used in construction of rooms which require good acoustic qualities such as auditoria and libraries.
Proprietary types of acoustic plaster developed in the 1920s included Macoustic Plaster, Sabinite, Kalite, Wyodak, Old Newark and Sprayo-Flake produced by companies such as US Gypsum. These superseded felts and quilts as a common preference of architects but were difficult to apply and so were superseded in turn by acoustic tiles.